The following abbreviations are herewith defined, at least some of which are referred to within the following description of the prior art and the present invention.                AWG Arrayed Waveguide Grating        DS Downstream, from OLT to ONT(s)        EPON Ethernet Passive Optical Network        FTTH Fiber-to-the-Home        GPON Gigabit-Capable Passive Optical Network        ONT Optical Network Termination        ONU Optical Network Unit        PON Passive Optical Network        Rx Receiver        SDH Synchronous Digital Hierarchy        TDM Time Division Multiplexing        TDMA Time Division Multiple Access        TRx Transceiver        Tx Transmitter        US Upstream, from ONT(s) to OLT        WDM Wavelength Division Multiplexing        
The current fiber-optic communication networks are reaching closer to the end-users at an ever increasing pace and with ever increasing bandwidths. Ultimately, these fiber-optic communication networks will reach all the way to the subscriber, i.e. fiber to the home (FTTH). Currently, these so-called fiber-to-the-x networks (x being home, building, curb etc.) can be realized with point-to-point (p2p) dedicated fibers to each end-user or with point-to-multipoint (p2 mp) passive optical networks (PONs) to multiple end-users. PONs are further divided into time-division multiplexed (TDM) PONs and wavelength-multiplexed (WDM) PONs or hybrids thereof. Examples of TMD-PONs are GPON and EPON. The term passive in PON comes from the fact that a passive splitter is used to achieve the p2 mp function between the central office equipment (optical line terminal, OLT) and the end-users (optical network termination, ONT). The passive splitter for the TDM-PONs is a power splitter while for the WDM-PONs the passive splitter is a wavelength splitter, often of the arrayed waveguide grating (AWG) type.
The WDM-PON when compared to the TDM-PON has several advantages (for example): (1) dedicated bandwidth to each end-user; and (2) communication privacy and much lower insertion loss when using the AWG splitter when compared to the TDM-PON's power splitter, which enables long reach. However, the WDM-PON has a major disadvantage in that each ONT must transmit at a specific wavelength. Since the logistics of having 32, 64 or more types of ONTs is not practical, wavelength adaptive ONT transmitters must be used. These types of ONTs are typically referred to as “colorless” ONTs. Contrary to the complexity of the multitude of WDM-PON architectures that have been proposed, the use of tunable lasers is widely considered as the best long term solution. However, apart from their current relative high cost, the problem of automatic tuning the ONT's laser transmitters must be solved. Once put into service, the ONT's laser transmitters must get the knowledge of what wavelength they should use for the upstream (US) communication with the OLT receivers.
There have been several reported solutions which can address the problem of tuning the US wavelength of ONT's laser transmitters. In one reported solution, higher layer communications are used between the OLT and ONT in which a downstream channel carries control information over an Ethernet link informing the ONT of which wavelength the ONT laser transmitter should use for the US communications. This reported solution has a drawback where it is id protocol specific and cannot be used when the Ethernet functionality (or some other layer 2 protocol) is not present, active or suitable for this type of management information. Plus, this reported solution cannot be used if the ONT only utilizes an optical layer 1. Also, the wavelength tuning functionality of the ONT laser transmitter is clearly an optical layer 1 issue thus it could be argued that this functionality should be handled at layer 1 and not at some layer 2 protocol.
In another reported solution, a method has been proposed where the ONT laser transmitter just tests every US wavelength until it receives information that indicates the ONT laser transmitter's signal has been received at the OLT. This reported solution has several disadvantages in that it has high power consumption, it is quite slow (e.g., 1 minute), and it risks corrupting the US communications of the other ONTs if the isolation of the AWG wavelength splitter (or other wavelength splitter) is inadequate. Accordingly, there has been a need to address the current WDM-PONs shortcoming associated with not being able to effectively wavelength tune or otherwise set-up an ONT laser transmitter. This need and other needs are addressed by the present invention.